BOSTON (CBS) — The Celtics don’t know how Gordon Hayward hurt his foot and they don’t know when he’ll be back in action. But Danny Ainge isn’t concerned about the latest injury that has sidelined the C’s forward.

Boston considers Hayward day-to-day after he sat out Wednesday night’s 109-103 win over the Mavericks in Dallas. Hayward will undergo another MRI on Thursday back in Boston, as the Celtics try to figure out what is causing the lingering discomfort in his left foot.

Listening to Ainge discuss the injury during his Thursday morning chat with 98.5 The Sports Hub’s Toucher & Rich, it doesn’t sound very promising.

“He’s day-to-day. He’s had this foot issues. When he was coming back from the hand he was doing a lot of training, and he has a toe/foot — right where you toe connects with your foot — just some pain. We’re trying to figure out what it is,” explained Ainge. “He had a cortisone shot and it actually made it worse. No one knows exactly what the issue is.”

While the discomfort is in Hayward’s left foot, Ainge doesn’t believe it is related to the devastating ankle injury that ended Hayward’s first year in Boston just five minutes into the season.

“This has nothing to do with that prior injury. This is just an annoying thing he’s going through right now,” he said. “We’ll figure it out.”

Hayward just returned after he missed a month of action with a broken bone in his hand. Head coach Brad Stevens said Wednesday the foot was bothering Hayward before that injury, but an MRI a few weeks ago didn’t show any damage.

“He was doing a lot of work, maybe too much, even. I don’t think Gordon knows exactly what it is that caused it,” Ainge said Thursday. “He practiced on Monday, but left a little early. He thought he’d be OK to play in Dallas but it just got worse.

Ainge also gave a quick update on guard Marcus Smart, who has missed the last two weeks with an eye infection. Smart is feeling better after a tough battle with a virus and is getting closer to a return.

“He had a bad case of an eye infection, but he’s getting much better,” explained Ainge. “He had a viral issue. He was sick, had the flu for four or five days through the process, so he was quarantined at home. He’s getting better, and I’m hoping he’s going to be healthy. He hasn’t been out of bed or played basketball in the last 10 days or so.”

Ainge said that Smart could be back for Boston’s Christmas Day game against the Raptors in Toronto, but added “that’s just a guess.”